Lime is an important mineral constituent of the food. Chos-sat showed in 1842 that pigeons fed upon a diet poor in lime suffered from disarrangement of the feathers, diarrhoea and thirst, and died in 8-10 months with soft bones. Subsequent experiments with a lime free diet have confirmed this result. Voit, Seemann, and Baginsky found that dogs fed upon flesh, fat and distilled water, appeared to be normal for a considerable time and increased in weight, but ultimately became weak and suffered from changes in the bones accompanied by a disappearance of inorganic material. In zoological gardens it has been found impossible to rear lion cubs until bone dust has been added to their dietary, in imitation of the natural state of carnivorous animals in which the bones are eaten with the meat. In some recent experiments by Chalmers Watson, changes in the bones have been described as the result of feeding rats upon a meat diet; the present writer has put forward the suggestion that these may be due, not to the meat as such, but to the fact that the diet is deficient in inorganic material, and has found that the general condition of rats fed upon meat is improved by the addition of a small quantity of calcium phosphate to the food. The amount of calcium absorbed from the alimentary canal is very small and is practically all deposited in the bones : human muscle only contains 01 grammes per cent (Katz). Experiments which have been made to determine the part played by calcium in rickets have not led to very definite conclusions. When there is digestive disturbance it has been found that less calcium is absorbed. Arndt found that calcium was less freely absorbed from boiled milk than from unboiled. The bones in rickets are deficient in calcium, but it is stated that the tissues are not, whereas in animals upon a lime free diet, both bones and tissues show a diminution. Calcium lessens the muscular activity of the intestinal tract, as was experimentally shown by MacCallum. This explains the well-known fact that hard water is liable to produce constipation.
The metabolism of phosphates has been supposed to be specially connected with that of nervous tissues, but up to the present experiment has shown little foundation for this conjecture. Mental work has no influence upon the excretion of phosphoric acid. Folin and Shaffer showed that in cyclic insanity the phosphates in the urine were increased during the attacks. Beddard and the writer have found (in an unpublished research) that in migraine there is an increased excretion of phosphates in the urine in the early part of the attack. This increase is, however, rapidly followed by a corresponding diminution, so that the total amount excreted is not influenced. Ordinary food contains a sufficient proportion of phosphates, and no evidence has been brought forward that the addition of more is of any advantage to the organism.